TY - JOUR
T1 - Role of strontium addition on the phase transition of lanthanum copper oxide from K2NiF4 to perovskite structure
AU - Yu, Ho Chieh
AU - Fung, Kuan Zong
N1 - Funding Information:
This work is financially supported by the National Science Council of Taiwan, ROC (Grant no. NSC 93-2120-M-006-004).
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/8/16
Y1 - 2007/8/16
N2 - Without Sr addition, the sintered La2O3 and CuO powder mixture in a mole ratio of 1:2 formed K2NiF4-structured La2CuO4 with excess CuO. When 15% of strontium was added, La2CuO4 transformed into the single perovskite La1-xSrxCuO2.5-δ phase with orthorhombic structure. As the strontium addition increased to 20%, the perovskite lattice changed from orthorhombic to tetragonal. These phase transitions may be attributed to the enhanced oxidation of the divalent cupper ions (Cu2+) to trivalent ones (Cu3+) by the strontium addition. Based on the electroneutrality in an ABO3 perovskite lattice, a divalent cation is unstable in the B-site cation sub-lattice when the A-site is occupied by a trivalent cation such as La3+. As strontium was added into the A-site cation sub-lattice, the oxidation of Cu2+ ion into trivalent Cu3+ ion was enhanced. The increase of Cu3+ concentration strengthened the electrostatic bonding (ESB) of copper ions with their neighboring anions. Consequently, the symmetrical tetragonal Sr-doped lanthanum copper oxide was obtained.
AB - Without Sr addition, the sintered La2O3 and CuO powder mixture in a mole ratio of 1:2 formed K2NiF4-structured La2CuO4 with excess CuO. When 15% of strontium was added, La2CuO4 transformed into the single perovskite La1-xSrxCuO2.5-δ phase with orthorhombic structure. As the strontium addition increased to 20%, the perovskite lattice changed from orthorhombic to tetragonal. These phase transitions may be attributed to the enhanced oxidation of the divalent cupper ions (Cu2+) to trivalent ones (Cu3+) by the strontium addition. Based on the electroneutrality in an ABO3 perovskite lattice, a divalent cation is unstable in the B-site cation sub-lattice when the A-site is occupied by a trivalent cation such as La3+. As strontium was added into the A-site cation sub-lattice, the oxidation of Cu2+ ion into trivalent Cu3+ ion was enhanced. The increase of Cu3+ concentration strengthened the electrostatic bonding (ESB) of copper ions with their neighboring anions. Consequently, the symmetrical tetragonal Sr-doped lanthanum copper oxide was obtained.
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U2 - 10.1016/j.jallcom.2006.09.004
DO - 10.1016/j.jallcom.2006.09.004
M3 - Article
AN - SCOPUS:34249751065
VL - 440
SP - 62
EP - 68
JO - Journal of the Less-Common Metals
JF - Journal of the Less-Common Metals
SN - 0925-8388
IS - 1-2
ER -